The invention relates especially to a method for the registration of respiration in human beings, preferably during sleep.
The invention also relates to the use of pressure-sensitive sensors that are known per se for the registration of temperature in connection with the aforementioned method.
Although the invention is described primarily in connection with measuring respiration during sleep, the principal idea of the invention could also be used during registration in connection with the flow and/or leakage of urine, the flow of blood and so forth.
Sleep is a periodic and, as a rule, rhythmically occurring state in which physical and mental activity are diminished.
Sleep brings about an immobility which is energy-conserving, the body's metabolism slows down, the muscles relax, breathing and the action of the heart become slower, and blood pressure falls.
In this state, a new supply of energy is built up and stored, and sleep is therefore a condition of life for living creatures.
It is therefore of crucial importance that the quality of sleep is the best possible and that disturbances can be remedied.
Different types of obstructions in the airways are among the problems which may lead to disturbed sleep for an individual.
These obstructions may be so serious that, in addition to a purely physical disturbance of sleep, they can result in a reduction and eventual stoppage of the oxygen supply with the consequences this has for the action of the heart, the cardiovascular system and other organs, in the short term and the long term.
In addition to the problems this causes for the individual in question, a problem such as snoring is also a real family or social problem because of the disturbance snoring can cause for other people in the period of sleep necessary for each individual.
In the registration of sleep in patients suffering from so-called sleep apnea, ie, the temporary cessation of breathing, techniques have been established which aim to register inhalation and exhalation.
One of the ways in which this is done is by placing one or more temperature-sensitive sensors between the nose and the mouth of the patient so that the sensors are subjected to the effect of the air which is breathed in and out, such as is described, eg, in U.S. Pat. No. 5,311,875.
Since the temperature of the inhaled air is different to that of the exhaled air, it is possible by means of suitable measuring and registering equipment to produce the signal emitted by the sensor in the form of a graphical respiration curve.
Together with the measurement and presentation of a number of other physiological parameters such as, eg, ECG, oxygen levels in the blood, EEG, eye movements, where especially the last-mentioned gives a good indication of the stage of sleep reached, respiration is also an important parameter for the diagnosis of a patient's condition.
Recently, the use of pressure registration at several points in the respiratory passage has been introduced.
The measurement of the pressure variations at predetermined points in the respiratory passage makes possible the localisation of obstructions in the sleep period. Pressure registrations of this kind are carried out by means of so-called micro-sensor catheters, ie, fine plastic tubes into which are mounted small pressure sensors.
Pressure-related signals, from both direct and indirect pressure which is exerted on these sensors, are conveyed to the sleep registration equipment and produced as pressure curves, eg, on the screen of a personal computer.
Since pressure sensors of this kind are usually more or less temperature-sensitive by nature, it is essential that the effects of temperature be compensated so that temperature fluctuations have a minimal effect on the pressure signals.
Of the known technology in this field, reference shall be made to U.S. Pat. No. 4,554,927, which describes a pressure and temperature sensor based on a piezoresistant element, made of a silicon crystal. However, the device described in this publication is unsuitable for measuring fluid flows. An essential aspect of this device is that it measures temperature in a separate, temperature-sensitive part which, however, is not pressure-sensitive.
For a general description of technology in this field, reference shall also be to the international application, WO 93/19669.
In contrast to the prior art, the present invention aims to utilise the effects of temperature in pressure sensors that are known per se.